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Publication numberUS3764866 A
Publication typeGrant
Publication dateOct 9, 1973
Filing dateDec 23, 1971
Priority dateDec 23, 1971
Also published asCA1095114A, CA1095114A1, DE2245679A1, DE2245679B2, DE2245679C3
Publication numberUS 3764866 A, US 3764866A, US-A-3764866, US3764866 A, US3764866A
InventorsJ Bonaventura, R Harshbarger
Original AssigneeXerox Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Corona generator
US 3764866 A
Abstract
A tungsten wire corona generator having a stable coating thereon for providing the generator with an extremely long life and a stable output.
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Description  (OCR text may contain errors)

United States Patent Bonaventura et al.

Oct. 9, 1973 CORONA GENERATOR Inventors: Joseph J. Bonaventura, Rochester; Raymond J. Harshharger, Ontario,

both of NY.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Dec. 23, 1971 Appl. No.: 211,542

US. Cl 317/262 A, ll7/231, 250/495 ZC,

Int. Cl. H0lt 19/00 Field of Search 317/2 R, 3, 4, 262 R, 317/262 A; 313/354, 355; 250/495 ZC, 49.5 GC, 49.5 TC; 117/231 [56] References Cited UNITED STATES PATENTS 2,922,883 l/l960 Giaimo, Jr. 317/262 A X 3,537,914 ll/1970 Cieplinski et a1. 117/231 X Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney-James J. Ralabate et al.

[57] ABSTRACT A tungsten wire corona generator having a stable coating thereon for providing the generator with an extremely long life and a stable output.

12 Claims, 1 Drawing Figure CORONA GENERATOR This invention relates to an inexpensive corona generator capable of producing a stable and uniform output and having the relatively long operating life.

More specifically, this invention relates to an electrical corona generator capable of producing a highly efficient discharge thus is well suited to effectively charge a receiving surface such as a xerographic plate or the like. This novel generator includes a corona emitting wire constructed of a tungsten material and having a surface coating thereon serving to extend the normal life of the generator and to smooth the corona deposited upon the plate receiving surface.

Many methods and devices have been disclosed in the prior art for producing a uniform electrostatic charge upon a photoconductive plate. One such charging device is disclosed by Vyverberg in U.S. Pat. 2,836,725, issued May 27, 1958, wherein an electrode in the form of a wire surrounded by an electrically grounded conductive shield is placed adjacent to a grounded receiving surface and a high voltage source connected to the wire wherein a corona discharge is produced. A corona discharge is produced when the generator is placed in close proximity to the plate and applied to the generator of sufficient magnitude to cause a breakdown of the ions in the air within the separating gap. As a result, charged ions are formed around the corona generator flow to the grounded plate surface and are deposited thereon to raise the plate potential to a relatively high level.

In the art of xerography it has been found that consistent reproductive quality can only be maintained when a uniform and constant charge potential is applied to the photoconductive plate. In many automatic machines of this type, a single wire generator, generally referred to as a corotron is employed. Generally, the efficiency of the corotron is dependent on many factors including the gap distance between the wire and the plate surface, the nature of the generating wire material, the diameter of the wire and other physical features thereof andthe amount of energy supplied to the corona emitter. Heretofore, most corotrons were constructed of platinum or some other precious metal because these materials displayed the ability to deliver uniform constant charging over a long period of time. As a consequence, these prior art devices were relatively expensive to construct and replacement costs were also high.

It is therefore an object of the present invention to provide a corona generating device constructed of a readily available inexpensive material.

A further object of this invention is to provide a relatively inexpensive corona generator exhibiting a highly stable output and having a relatively long operating life.

A still further object of this inventin is to improve the corona generating art.

These and other objects of the present invention are attained by means of apparatus for charging the surface of a photoconductive plate which includes a corona generating wire, a source of electrical energy being operatively connected to the generating wire to cause the wire to emit a corona discharge, the wire generator being constructed of a tungsten base material having a high temperature oxide coating thereon which is extremely stable and non-spalling within the operating range of the generator.

For a better understanding of the present invention as well as other objects and features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawing wherein the drawing illustrates a perspective view of a corona generating apparatus having a corona emitting wire fabricated in accordance with the teachings of the present invention.

Referring in particular to the attached FIGURE, there is illustrated a corona generating device containing a generator wire 25 of the present invention for depositing an electrostatic charge on the surface of a moving photoconductive recording material. Illustrated in the FIGURE is a xerographic plate 10 made up of a photoconductive insulating material I] placed upon a grounded conductive substrate 12 with the plate being arranged to move along a predetermined path of travel in the direction indicated. The corona generating unit, generally referred to as 15, is positioned above the plate surface and is arranged to deposit an electrical charge thereon as the plate surface moves in the direction indicated. The corona unit includes a shield member 17 which substantially encloses one or more corona generator wires 25 19. The shield is preferably made up of an electrically conductive material that is placed at a ground potential. A slit 20 or opening is formed in the bottom of the shield opposite the moving photoconductive surface and provides a path by which a flow of ions discharged by the generator are directed towards and deposited upon the moving plate surface. For further details regarding the structure of this type of corona generating unit, reference is had to the disclosure contained within the aforetomentioned Vyverberg patent.

The corona generating wire is connected by suitable means such as electrical connector 21 to a high potential source 23. The corona wire utilized in the present embodiment is connected directly to the positive terminal of the power source whereby a positive ion discharge is placed on the plate surface. However, it should be clear that an opposite arrangement can be employed to obtain a negative discharge. Basically, the generator is constructed of a fine wire between 0.003 and 0.006 inches in diameter made of a high quality tungsten being 99.95 percent pure. The wire preferably has a strength of about 280,000 psi. minimum and be capable of being elongated 1.4 percent over a 10 inch length when tested by ASTM method F219 (1) utilizing a cross head speed of approximately 1 ii inches per minute.

Normally, a pure tungsten wire generator of this nature will initially exhibit extremely good corona generating properties. However, after a very short operating period, the uniformity of output, i.e. the distribution and amount of corona generated by the wire, becomes erratic and the generator exhibits signs of early electrical breakdown. The reason for this short operating life is thought to be caused by loose randomly dispersed tungsten oxides which form on the wire surface at the relatively low operating temperatures. These low temperature oxides are found to be metastable and correspondingly, cause an unstable discharge to be produced by the generator. Furthermore, the mechanical properties of these low temperature oxides are such that the oxides invariably spall from the wire in an uncontrolled manner further aggravating the problems involved.

In the present invention, all the shortcomings previously associated with a tungsten wire corona generator have been overcome to provide a generator which is inexpensive to produce and which has an extremely long operating life and the capability of delivering an extremely uniform stable output over its entire operating life. To produce this truly novel result, the generator wire is specially treated to form an extremely smooth, uniform and tough coating thereon which will remain relatively stable throughout the operating life of the generator.

To produce this generator, a substantially pure tungsten wire 18 having the beforementioned properties is chemically cleaned to remove foreign matter and grease from the surface of the wire and the wire stress relieved. Any suitable process commonly known and used in the art can be herein employed. The wire is then placed within an electrical oven and the oven heated to a temperature in excess of 600C in air. A wire having a diameter of approximately 0.0035 inches, when heat treated in this manner for approximately minutes, will be provided with an oxide coating 19 which is between 1.5 and 3.5 microns thick. An analysis of this coating shows that it is made up of high temperature oxides including W0 W0 and W 0 Generating wires produced in this manner have been found to have an extremely stable coating which serves to prevent physical changes in the wire at the operating temperature and provides for an extremely stable output and long operating life. The high temperature oxide coating thus formed is relatively tough and is capable of readily withstanding light scraping with a metallic instrument. Spalling of the coating occurs only when the generator wire is permanently deformed or kinked. In fact, the wire can be bent about a A inch diameter rod without disturbing the coating in any manner.

In order to ascertain the capabilities of the generator of the present invention, a test fixture was constructed by which the output of the generator could be evaluated and compared to similar generators constructed of other materials. The fixture basically consisted of a rotatably mounted grounded xerographic plate in drum configuration having a corona wire support mounted adjacent thereto for supporting a wire generator transverse to the drum surface. The wire generator was arranged to be electrically coupled to a high power source of electrical energy with the wire being supported above the drum surface at a distance whereby the corotron drew approximately 325 micro amps of current while charging the plate surface to a potential of approximately 800 volts. A thin brass strip was helically wound about the drum so that the strip continually monitored the bare plate current flow between the generator wire and the plate as the drum rotated under the generator. The brass strip was electrically brought out to a recording device by means of a slip ring and the recorder arranged to record data at approximately mm/sec. Under these operating conditions, a bare plate current of approximately 50 micro amps was initially recorded and the amplitude of the current deviation from this initial current reading was graphically registered.

A heat treated tungsten wire was placed within the test apparatus and continually operated for a period of approximately 250 hours. Periodic traces of the bare plate current reveal that the output of the heat treated generator remain relatively stable and unchanged over the test period. Subsequent to this test, a second corona generatorpf untreated tungsten wire similar in dimensions to that previously tested was placed within the fixture and an operating current placed thereon. After approximately 25 minutes of operation, the untreated tungsten generator began to produce a non-uniform and unstable output and thereafter the generator continued to electrically fail.

Next a comparison test of a heat treated tungsten generator and a platinum generator having similar physical properties was made. The wires were properties arranged in the fixture so as to produce the same bare plate current output at the drum surface. After approximately 256 continuous hours of operation, no differences in the performance of the platinum wire generator and that of the treated tungsten wire generator could be discerned.

While this invention has been described with reference to the structure herein disclosed, it is not confined to the details as set forth and this application is intended to cover any modifications or changes that may come within the scope of the following claims.

What is claimed is:

l. A device for emitting a discharge of corona including a tungsten electrode being arranged to emit a corona discharge,

a coating overlying at least the discharge region of said electrode being formed of a high temperature tungsten oxide that is stable during periods when said electrode is emitting corona whereby a uniform discharge of corona is produced over an extended period of time.

2. The apparatus of claim 1 wherein the tungsten electrode is formed of a material that is at least 99 percent pure.

3. The apparatus of claim 2 wherein the oxide formed on said electrode includes the oxides WO and W 0 4. The apparatus of claim 3 wherein the oxide coating is of a thickness of about or greater than one-half a micron.

5. The method of producing a corona emitting electrode which is capable of producing a stable output over an extended period of time including providing an electrode of relatively pure tungsten,

and

oxidizing said electrode by heating the electrode in air to a temperature at or about 600C for a period of time Sufl'Tcient ttEFat tfiionina generating surface with a tungsten oxide layer.

6. The method of claim 5 wherein the coating formed on said electrode includes the oxides W0, and W 0 7. The method of Claim 5 wherein said electrode is precleaned prior to oxidation to remove impurities from the surface of said electrode.

8. The method of claim 5 wherein said electrode is heated at or above 600C for at least 10 minutes.

9. The method of claim 5 wherein said oxide coating is formed to a thickness which is at least one-half of a micron.

10. The method of claim 5 wherein said electrode is formed of a tungsten material which is at least 99 percent pure.

11. The method of producing a corona emitting electrode that is capable of producing a stable output over an extended period of time including producing an elongated tungsten wire formed of a relatively pure material,

cleaning the surface of said tungsten wire to remove impurities therefrom,

oxidizing said tungsten wire by heating said wire in air to a temperature at or above 600C fora period of time sufficient to form an oxide coating thereon 5 w18O49- which is between one-half and three and one-half

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2922883 *Mar 3, 1955Jan 26, 1960Rca CorpElectrostatic charging means and method
US3537914 *Jan 19, 1968Nov 3, 1970Hewlett Packard CoPassivation of thermal conductivity filaments
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4096543 *Oct 26, 1976Jun 20, 1978Mita Industrial Company, Ltd.Corona discharge device with grid grounded via non-linear bias element
US4110614 *Dec 17, 1976Aug 29, 1978Xerox CorporationCorona device
US4542977 *Sep 15, 1983Sep 24, 1985Konishiroku Photo Industry Co., Ltd.Method and apparatus for separating recording paper from image retaining member
US4837658 *Dec 14, 1988Jun 6, 1989Xerox CorporationLong life corona charging device
US4910637 *Oct 23, 1978Mar 20, 1990Rinoud HannaModifying the discharge breakdown
US5028779 *Nov 1, 1984Jul 2, 1991Xerox CorporationCorona charging device
US6605165 *May 26, 2000Aug 12, 2003Canon Kabushiki KaishaMethod of manufacturing discharge wire
US6917776Jun 9, 2003Jul 12, 2005Canon Kabushiki KaishaDischarge wire, method of manufacturing discharge wire and electrification device
CN104646566A *Feb 4, 2015May 27, 2015安徽意义环保设备有限公司Corona wire bending frame
EP1055972A2 *May 26, 2000Nov 29, 2000Canon Kabushiki KaishaDischarge wire, method of manufacturing discharge wire and electrification device
EP1055972A3 *May 26, 2000Jan 14, 2004Canon Kabushiki KaishaDischarge wire, method of manufacturing discharge wire and electrification device
Classifications
U.S. Classification361/230, 250/324, 427/120
International ClassificationH01T19/00, H05F3/04, G03G15/02, G03G13/00
Cooperative ClassificationH05F3/04, G03G15/0291
European ClassificationH05F3/04, G03G15/02